The present invention relates generally to the field of optical observation and tracking and more particularly to inertially-aided optical observation and tracking systems.
The alignment stability which can be maintained between the inertial reference system and the optical system in an inertially-aided optical system is a critical performance limiting factor. Frame deformation internal to the optical sensor, e.g. a telescope, adds directly to system errors. Such deformation may result from thermal or motion effects from the sensor vehicle. In the prior art, methods for accommodating such deformation-induced error employed active alignment systems which optically detect deformation within the optical sensor and respond with positional changes or data manipulation in an attempt to correct for such deformations.
In the area of large observing telescopes and in high energy laser pointing tracking applications, the prior art devices are particularly sensitive to relative bending or misalignment of their elements with respect to the inertial reference frame. For example, the optical elements and associated support structures of very large observing telescopes deform when they are rotated with respect to the gravitational field. If this deformation cannot be detected and measured and then offset during a trajectory tracking operation, then motion is attributed to the target which in fact does not exist. In high energy laser trackers, similar problems exist.
In another area of the prior art, updating techniques used in vehicle-borne inertial measurement units (IMU's) employ a known surveyed point with a corner reflector and a laser tracker to measure the error attitude at the vehicle. Errors attributable to the tracker pointing and also to the mechanical and electrical interfaces between the tracker and IMU, pose service performance limitations.
Additionally in the prior art, for the problem of optically guided interceptor missiles one substantial error contributor has been the relative misalignment existing between the optical system and an inertial reference system. Generally in such systems, the target-to-be-intercepted is tracked by the optical system. However, that vehicle must be referred to a stable inertial reference frame for purposes of interceptor guidance. In tracking systems which employ an optical sensor, one problem in the prior art is obtaining high quality tracking data for a target with respect to inertial space. Such data can be obtained when the optical field which includes the target also includes a reference star (providing data representative of the relative difference in position between the target and the reference star position). In general, however, it is rare to find a convenient star in the sensor field of view that is suitable for use as a reference.
It is an object of the present invention to provide an apparatus for minimizing the relative misalignment between an optical system and an internal reference system.
Another object is to minimize the effect of optical sensor frame deformation in an inertially aided optical system.